Measuring apparatus



March 8, 1960 R. B. BEARD 2,927,888

MEASURING APPARATUS Original Filed Feb. 8. 1956 2 Sheets-Sheet. 1

I i S INVTOR. RICHARD B. BEARD ATTORNEY.

March 8, 1960 R. B. BEARD 2,927,388

MEASURING APPARATUS 2 Sheets-Sheet 2 Original Filed Feb. 8, 1956 IFIG.4

PRESS. RELIEF RESERVOIR Wd.

FIG. 5

FIG.6

INVENTOR. RICHARD B. BEARD BY fl RESERVOIR ATTORNEY.

United States Patent MEASURING APPARATUS:

Richard-B. Beard, Philadelphia, Pa, assignorto Minne- "apoli's fioneywell Regulator Company; Minneapolis;

Minn. a corporation of Delaware Original application February 8,1956, Serial No.=564, 20 7,

now Patent No. 2,882,212, dated April 14,1959, Di: vide d-andthisapplication June 17, 1958', Serial No. 742,524,

3 Claims. (Cl. 204195) This application-is a division of co-pending application. Serial No. 564,207, filed February 8, 1956,; in the nameo'f Richar d B. Beard,- now Patent 2,882;2 l2,- patented- April14, 1959.-

A general object of the present invention is to provide" a new and improved apparatus for measuring the ion concentration of a preselected ion in a liquid. More specifi-j ice member with means for enhancin'g the movement of i'th'e cally, the present invention is concerned with a new and improved apparatus .for measuring the ionic concentration of-a preselected ion in a liquid by means of anion permeable membrane in combination withmeans for measuring the rate of permeation of the preselected ion through the membrane. V

The preparation of many chemical solutions requires the measurement and control of the ionic concentration in thesolution in order to attain a desired end'product- The; measurement of ion concentrations has been achieved l irithe past by devices of the electric potential generating type operating upon the principle of an electrolytic cell. These types of devices are extremely delicate and thereby subject to'destruction underordinary conditionsof use. Further, these devices require considerable service'andmaintenance in order to keep them in an operating condi tion. The present inventionisdirected to an improved ion concentration measuring apparatus which overcomes.- the operating difficulties encountered with presently} known types ot-ion concentration measuring devices.

It is well known that hydrogen will diffuse through certaintypes of'metals very readily. This principle hasbeen used in the measurement of hydrogen partial pressures in atmospheres under analysis.- One metal which-is particularly adapted for passing hydrogenis palladium;--

The rate at which hydrogen will pass through palladium is a function of the temperature as well as the-concentra tion of the hydrogen present'in the atmosphereundera ys The present invention isdirected to an apparatus em ploying the selective permeability of anion permeable member, such as palladium, and applying this principle" to the-measurement of ion concentrations in 'afiuid ora liquid. Theion permeable member is arranged with-respect to the liquid under'analysis such that the ions-prey ent in the liquid tend to migrate to the permeable mem her and diffuse therethrough at-a-rate which'is-a direct} It -iis accordingly .a more specific object of-the-presentinventionto provide= a new and -irnproved ion concen tration measuring apparatus employing an ionapermeable s selected ion toward the permeable member duringithe measuring operation;

Still anotherobject of the present invention isto preevide a new and "improved. ion concentration measuring? apparatusjincorporating' a selectively permeable member. arranged'for positioning in'a solution where a selectedl ion concentration isQto be measured andapplyingam electrical biasing potential which is elfective toflcause. migratio n of the selected ion toward said member to.

enhance the permeation of the'selected' ion throughythe.

member in combination with means fo r measuring. th'erate of permeation," said rate being indicative ofthe ion. concentration in said fluid.

A- still furtherjmore specific object of the-present in? vention' is to provide anew and improved ion concentraw. ti on' measuring. apparatus incorporating means for. pro: ducing a pressure indicative of the ion concentration.

Stillanothermore specific object of the present inven-- tion is to provide a new and improved ion concentration, measuring apparatus for a solution incorporating a pair of sensing means which are-adapted to be connected so as to eliminate ambient temperature and pressure effects. onthe measuring apparatus. I

The various features'of novelty which characterize the invention are pointed out with particularity in the claims. annexed to and forminga part of this specification. For a better understanding of the invention, its advantages,

and specific objects attained with its use, reference should I l be had to theaccompanying drawing, and'descriptive; .matter inwhich there is illustrated and 'described,.pre-j.

ferred embodiments of thelinvention. 7

Of .the drawings: Fig. 1 is a diagrammatic showing of a representative.

form of the present invention; I Fig, 2 is a modified form of the apparatus of Fig; 1'

incorporating a .difierent means for measuring the rate ofji permeation through the sensing membrane;

Fig.3 'shows a further modified form of apparatus for. measuring the permeation rateof the ion concentration sensing element;

Fig. 4 shows 'stillianother modified form of permeation. rate measuring apparatus;

Fig: 5 "shows a formgiof the present invention adapted f'. for use where ambient temperatures and pressures must; be eliminated: and

Fig; 6 showsstill another modified form of apparatus .1 for measuring the permeationrate of the ionconentration sensing element; 7 v

Referring firstto Fig, 1, the numeral '10 represents-a container in which thereis locateda solution whose ion concentration is to be determined. The solu'tion ll is'... arranged to be supplied thereto by an inlet conduit 12!; andremoved jtherefrom' by 'anoutlet condu'it'13. Positionedwithin'jthe'solution;;10"are a pairv of electrodes 15" and '16: Electrode 15 "is an electrical, conductor while/'5 the electrode16fis'a'hollow'ion permeable tube}; In case,

of}; solution where the. hydrogen" ion concentration is to be-meas ured, the tube-16 would preferably be formed-jot? palladium; Injthe, case where oxygen ion concentration isto be determined,'the tube :16inig'ht well take the form of a silver tube; A .battery' 17 is shown connected to" supply a biasing potential between the CICCiIOdB'S'ilSffitld 16.. The insideof 'the electrode tube "16is arrangedffdr I? connection ,to an outlet 18,' the outlet .18 comprisingga j gaseous permeable tube or membrane arrangedfi'to be heated by an electrical heater19. Also connectedtoiit output of the, tube 16 is a pressure transducer'zlljwhosef output is adapted to position a rheostat21'1iniseries withfj, theheater19. The rheostat in turn will regulateth'e', rent flowing from a power source"22;f to 'theflhater, 2;

- -In -serieswith the'ieedline to the heater-19 ism-runner resistor 23. The potential drop across the resistor 23 is applied to a suitable indicating and recording instrument 24, the latter of which may be conveniently calibrated in terms of ion concentration.

In considering the operation of Fig. 1, it is first assumed that the solution 11 is an electrolyte having a hydrogen ion concentration which is to be determined. Since the hydrogen ion concentration is to be determined, it is essential that the tube 16 be selected to be of the type which will be capable of readily difiusing hydrogen therethrough. Further, it is essential that the battery 17 beso polarized that the hydrogen ions will be attracted to the electrode 16. As the hydrogen ions are moved toward electrode 16, they are sorbed on the surface thereof, diffusedtherethrough, and desorbed on the inside thereof. This process or phenomena is a one way process so that the pressure within the tube 16 will continue to build up at a rate dependent upon the rate that the hydrogen ions diffuse into the tube. As the phenomena is irreversible, it is essential that there be an outlet for the hydrogen built up in the tube 16 and this is provided by the outlet 18. This outlet 18, in the case of hydrogen, is preferably formed of palladium and heated to readily pass the hydrogen into the atmosphere or into some other desirable space. The rate at which the gas will escape from the outlet 18 is determined by the temperature thereof and this is controlled by the amount of heat supplied thereto by the heater 19. The heater 19 is'controlled by the pressure transducer 20 acting through the rheostat 21. The transducer 20 will try to maintain a constant pressure within the tube 16 and as the pressure increases, the transducer will increase the amount of heat supplied to the outlet 18 so that the pressure will drop. Conversely, if the pressure should decrease below the desired value, the transducer 20 will reset the rheostat 21 until the pressure within the system is back at the desired value. As the pressure within the system will be a direct function of the rate at which the hydrogen is being diffused into the tube 16, the maintaining of a constant pressure, as by the present form of the apparatus, will provide a means for determining the actual permeation rate through the tube 16. This is determined by the amount of heat required on tube outlet 18 to maintain a desired pressure within the system. The amount of heat may be measured by measuring the voltage drop across the resistor 23 in series with the energizing source 22 so that the voltage drop'thereacross will be indicative of the current flow to the heater 19. This current flow will in turn be a function of the rate at which the hydrogen ions are being difiused into the tube 16.

Should the ion concentration in the solution 11 increase, the ions will diffuse into the tube 16 at a greater rate and thereby tend to increase the pressure within the tube and the rest of the pressure system. Thetransducer 20 will indicate that pressure increase and will readjust the rheostat so that more heat will be added to the outlet 18. Increased heat applied to the outlet 18 will decrease the pressure in the system to a desiredvalue. The current to the heater 19 necessary to maintain that desired pressure condition will produce a voltage across the resistor 23' indicative of the ion concentration of the solution 11.

Should there be a decrease in the ion concentration within the solution 11, the pressure within the tube 16 will drop and the transducer 20 will respond to this pressure drop. The transducer 20 will be effective to reposition the rheostat 21 to decrease the amount of heat applied to the outlet 18 and thereby further restrict the outlet 18 so that the pressure will build up to the desired value. The decrease in the current flow to the heater 19 to effect this temperature decrease will produce a change in the signal across resistor 23 to thereby indicate the decrease in the ion concentration. 7

In the present form of the apparatus shown in Figure 1, it isv desirable that the current concentration between the electrodes 15 and 16 remain constant. This requires constant spacing between the electrodes and the use of a constant current source by way of the battery 17.

The apparatus of Figure 2 involves the same basic components as that of Fig. l and accordingly, corresponding components carry corresponding reference charac ters. The principle distinction between the apparatus of Fig. 1 and that of Fig 2 lies in the use of a pressure system outlet 18 whose temperature is maintained constant as by a temperature regulator 30. Further, the current density between the electrodes 15 and 16 is controlled by a rheostat 31, the latter of which is arranged to be adjusted in accordance with the partial pressure of the hydrogen present within the outlet tube 18. This hydrogen pressure is determined by a transducer 32. The transducer 32 comprises a pair of thermocouple elements 32A and 323. One of these elements comprises a hydrogen concentration sensitive element whose thermoelectric output is proportional to the pressure of the hydrogen in the tube 18. This transducer 32 may well take the form of the transducer disclosed in the copending application of Richard B. Beard, Serial No. 389,418.

In series with a rheostat 31 is a resistor 34, the latter of which has a voltage drop thereacross proportional to the current flowing between the electrodes 15 and 16. This signal across the resistor 34 is applied to a suitable indicating and recording instrument 35. Also ;in series with resistor 34 and rheostat 31 is a source of power 17A, the latter not being of the constant current type.

The operation of Fig. 2 is basically similar to that of Fig. 1 in that current flowing between the electrodes 15 and 16 will cause a migration of the hydrogen ions therein so that the hydrogen will diffuse into the inside of the tube 16 and build up a pressure therein. The hydrogen passing into the tube 16 is passed out of the tube by way of the outlet 18, the latter of which is now acting as a constant restricted outlet whose temperature is maintained constant so as to maintain the constant outlet restriction characteristic. The pressure of the gas within the outlet chamber 18 is arranged to be measured by the transducer 32 which, as mentioned above, is of the thermoelectric type. This type of transducer is adapted to produce an output potential from a thermocouple positioned within the chamber which is proportional to the actual pressure of the hydrogen present within the chamber. The transducer 32 will then adjust the rheostat 31 so that the current flowing between the electrodes 15 and 16 will maintain the desired pressure within the system.

Should the ion concentration increase in the solution 11, the pressure within the chamber 16 will increase. This pressure increase will be indicated by the transducer 32 which will reset the rheostat 31 to decrease the current flowing between the electrodes 15 and 16. This decrease will result in a drop in the potential across the resistor 34 and the resultant signal recorded by the instrument 35 will then be proportional to the ion concen tration in the solution.

If the ion concentration should decrease, the pressure within the electrode 16 and chamber 18 will decrease and this decrease will be sensed by the transducer 32 which in turn will adjust the rheostat so as to increase the current flow between the electrodes 15 and 16. The increased current flow will bring the pressure within the system back to the desired value and the change in current flow will be indicated by the potential drop across the resistor 34. This will in turn be indicated by the instrument 35 with the indication being proportional to the ion concentration of the solution.

The apparatus of Fig. 3 shows another form of apparatus for measuring the rate at which the preselected ion is diffused through electrode v16. In this figure, the components corresponding to the components of Fig. I carry corresponding reference characters. Added to the present system for measuring the rate of diffusion is a flowmeter 40 connected in the output,conduit 45,of,the

permeable electrode 161 The outlet from the flowmeter 40 flows through an outlet conduit46 which isworkin g against a constant head pressure, in a containerf47 which. has liquid extending up over the end of the conduitf'46i The output signal from thefiowmeter 40 is arranged for'connection to a suitable indicating and recording 'instrurnent 48.

In operation, the basic functioning of the apparatus. of Fig. 3 is the same as that of Figs. 1 and 2 inthat the current passing between the electrodes 15 and 16. will serve to move the hydrogen ions therein toward the electrode 16 so that these hydrogen ions may pass therethrough. The rate at whichthis diffusion will take place will be directly proportional to the concentration of the hydrogen ions in the solution 11. 1f thecurr'ent between the electrodes is maintained constant by 'the battery.17, the only variable in the. system will. be the ion concentration in the solution 11. This will meanthat the flow rate passing through the output conduit, 45 will be a direct measure of the ion concentration. so that the output of the meter 40, when.- indicating thislfiow rate, may be calibrated directly in terms of ion concentration.

' The apparatus of Fig. 4 is again of the samebasic nature as the apparatus of Fig.1 and-corresponding componeuts carry corresponding reference characters. Added to the apparatus of Fig. 4 is a reservoir 50. which connected to the output conduit 45. of the permeable electrode 16. The outlet of the reservoir 50 is controlled by a valve 51and this valve 51 is in turn controlled. by.

a timer 52. The pressure within. the reservoir. 50. .is measured in accordance withits rate of change by. a pressure rate of change to electric signal transducer;5 3. This'latter transducer is arranged to have its output electrically connected to a suitableindicating and recording instrument 54.

In considering the operation of the Fig. 4 apparatus, it is first. assumed that there isa constant current fiow-.

ing between the electrodes 15fand 16 and thatv the hyaccordance with the ion concentration of the solution 11. As the hydrogen ions diffuse into the electrode 16, the pressure in .the.output reservoin.50;will buildup and the rate at which .it builds up will .be a direct function of the rate at which the ions are diffusing through the electrode 16.. The transducer 53-will measure the rate of change of the pressurerinthe reservoir 50 and produce. an electricalsignal inuaccordance with that rate of change which is recorded by the instrument 54. As the pressure in the reservoir will continue to build up, his essential that after a period of-time the pressure within the chamber should be let out and a new measuring cycle started. This may be controlled by the periodic opening of the valve 51 by the timer 52. For safety purposes, it may well be advisable, to include with the apparatus a pressure overload relief valve 55.

It will be readily apparent that in the apparatus of Fig. 4 that if the ion concentration goes up in the solution 11, the rate of diffusion of the ions through the electrode 16 will be greater so that the rate of change of the pressure in the reservoir 50 will be greater. Conversely, if the concentration of the ions in the solution 11 should decrease, the rate of diffusion into the reservoir will decrease. These changes will be appropriately indicated by the instrument 54 to indicate directly the ion concentration of the solution 11. p

The apparatus of Fig. 5 is a modification wherein the ambient temperature and pressure effects may be eliminated. In this form of the apparatus, there are provided a pair of electrodes of the selectively permeable type 60 and 61. These two electrodes may be positioned on opposite sides of the container with a further electrode 62 positioned therebetween. A battery 63 is arranged to apply a potential between the electrodes 60 and 62. while electrical signals areapplied to a suitable indicating and 4D,. drogen ions are being diffused into the electrode 16in I recording instrument .70. The outlet for the. conduit 65; is a .selectively permeable .outlet 71 havingia heater 72 associated therewith. The outlet for thecouduit.66 is a; selectively permeable output .73, the latter having alleatelj 74. The temperature ofthe output .73..is arranged to bev controlled by atemperature controller.r75shaving,an.inputt thermocouple 76, and anio'u'tput' connected to alrheostat, 77, the. latter of which is in series with the. heaters 12, 74, andv a. source of powems. r

The operation of'the apparatus of Fig, 5 is dependent. uponf'the ionic Vdifi'usion characteristics of the. aforemen; tione d apparatusdisclosedlin Figs. Lth'rough 4, The. useof two suchusystemsin. asingle measurement permits the. apparatus to be bot h temperature and pressure come. pensated. The current flowing between the electrode 162. andthe electrode 60.. is effective to cause a migrationof the. hydrogen ionsto the electrode 60 andtherethrough into the output conduit 65 and thence ,to the outlet The current from battery. will be flowing between the electrode 62 .and the electrode 61tol cause a migration ofthelhydrogen ions to the electrode 61 andthencetherethroughto. theconduit 66. The conduit 66 isinlturn arranged .to be bled bythe outlet 73. Both the outlets 71 and73 arecontrolled to effectivelythesametemper.

the same .from. their respective conduits 65 .and 66.

' Thebattery 64 is larger than the-battery 6'3sso to establish different current densities between. the respec-c; tive electrodes. electrodes 62fand 60 is arranged to be somewhataless, than the current density between theelectrode '62; and the electrode 61.. This for .afgreatertnuinber of hydrogen ions to diffuse through. the electrode. 61 so that the pressure. inthe output con duit 66 willbe higher than the pressure in. the conduit 65. By opposing. the output pressures in, the, conduit. 65' against the pressure inthe conduit 66, a differential pres sure lsignal is produced on the output ofthetransdueers, 67 and. 68 whichis indicative only of the ion concentra;

tion. This will be readily apparent when vit-is noted; that both ambient pressures and temperatures will be acting t the same on the pressure systems associated withthe electrodes 60 and 61s will be indicated by an appropriate change in the output of the pressure transducers 67 and 68 and there will be :a resultant change in the indication of the instrument 70. Conversely, if the ion concentration of the solution 11 should decrease, the rate of permeation in the electrodes 60 and 61 will, decrease with the decrease being greater in the electrode 60 than in the electrode 61. This will result in a pressure change in the conduits 65 and 66 which, when reflected through the transducers 67 and 68, will produce an indication on the instrument 70 indicating a decreased ion concentration in the solution 11.

The apparatus of Fig. 6 is a modification of that shown in Fig. 4 and corresponding components carry corresponding reference characters. In this figure, a pressure sensitive relay switch means has been added and this switch meanscomprises a pressure responsive unit which opens an electrical switch contact at a pressure P; and

Thus, the current density between the.

will meanthat there is a tendency closes the switch contact at a pressure P In series with the output of the switch means 80 is the valve 51 and a counter 82.

The apparatus of Fig. 6 operates basically the same as that of Fig. 4 in that the rate at which the pressure builds up in the reservoir 50 is a function of the ion concentration in the liquid being analyzed. When the pressure builds up to a given pressure P the relay switch means 80 will close to complete an energizing circuit to the valve 51 so that the valve will open to bleed out the pressure in reservoir 50. When the pressure has dropped to pressure P the relay switch means 80 will open its contacts to deenergize the valve 51. The pressure will then build up again to pressure P at which time the valve 51 will again be opened. It will be readily apparent that the rate at which the valve 51 is opened and closed will be a function of the ion concentration of the liquid being examined. This rate may be determined by noting the reading of the counter 82, which is actuated each time the valve 51 is energized, over a given period of time. The differential of the pulse rate of valve 51 may also be used to indicate the ion concentration. This form of the apparatus is very simple in construction and thereby adapts itself to a very inexpensive, but nonetheless accurate, form of ion concentrationmeasurement.

The principles of the present invention have been applied primarily to the measurement of hydrogen ion concentration. However, it will be readily apparent that the principles are equally applicable to other ion concentration measurements wherein the ions of the solution will diffuse through an associated electrode placed within the solution; In the case of an oxygen ion concentration measurement, a silver electrode may well be placed in the solution in the manner set forth in the foregoing description. It will be readily apparent that the polarity of the current source must be such as to cause a migration of the oxygen in the form of hydroxyl ions toward the silver electrode. Further, the outlets of such apparatus must be selected of a corresponding material, such as silver, in order to achieve a desired relation of the flow of the diffused oxygen through the pressure system.

While, in accordance with the provisions of the statutes, there has been illustrated and described the best forms of the invention known, it will be apparent to those skilled in the art that changes may be made in the form of the apparatus disclosed without departing from the spirit of the invention as set forth in the appending claims, and that in certain cases, certain features of the invention may be used to advantage without a corresponding use of other features.

Having now described the invention, what is claimed as new and for which it is desired to secure by Letters Patent is:

1. Apparatus for measuring oxygen concentration in a fluid having oxygen and non-oxygen constituents and having in combination: a container having an inlet thereto and an outlet therefrom for accommodating said fluid; an extended length of small-diameter, oxygen-permeable tube having a closed end and an open end, said oxygenpermeable tube barring the non-oxygen constituents of said fluid from the inside of said tube, so that the partial pressures of said non-oxygen constituents are not exerted on the inside of said tube; means for holding said smalldiameter tube within said container, whereby the exterior surface and closed end of said tube are in contact with said fluid flowing through said container; an electrode within said container in contact with said fluid flowing through said container; at source of electrical potential connected to said electrode and to said tube and so polarized that the hydroxyl ions are attracted to said tube, the oxygen molecules sorbed on the surface thereof, diffused therethrough, and desorbed on the inside thereof; an oxygen-permeable membrane connected to the inside of said tube so as to receive the desorbed oxygen therein at a partial pressure, said oxygen-permeable membrane barring the non-oxygen constituents of the surrounding atmosphere from the inside of said tube, so that the partial pressures of said non-oxygen constituents are not exerted in the inside of said tube; an electrical heater arranged to heat said membrane and thereby to vary the oxygen permeability thereof; a source of electricity connected to said heater to supply power thereto; and means responsive to the pressure of the desorbed oxygen on the inside of the tube and on the inside of said membrane and operable to vary the power applied to said heater and, consequently, to vary the amount of said oxygen which passes through said membrane to the surrounding atmosphere.

2. Apparatus according to claim 1 wherein the oxygenpermeable tube is composed in major part of silver.

3. Apparatus according to claim 1 wherein the oxygenpermeable membrane is composed in major part of silver.

References Cited in the file of this patent UNITED STATES PATENTS Keeler Nov. 13, 1923 Craig June 29, 1948 Hulsberg Mar. 9, 1954 OTHER REFERENCES 

1. APPARATUS FOR MEASURING OXYGEN CONCENTRATION IN FLUID HAVING OXYGEN AND NON-OXYGEN CONSTITUENTS AND HAVING IN COMBINATION: A CONTAINER HAVING AN INLET THERETO AND AN OUTLET THEREFROM FOR ACCOMODATING SAID FLUID, AN EXTENDED LENGTH OF SMALL-DIAMETER, OXYGEN-PERMEABLE TUBE HAVING A CLOSED END AND AN OPEN END, SAID OXYGENPERMEABLE TUBE BARRING THE NON-OXYGEN CONSTITUENTS OF SAID FLUID FROM THE INSIDE OF SAID TUBE, SO THAT THE PARTIAL PRESSURES OF SAID NON-OXYGEN CONSTITUENTS ARE NOT EXERTED ON THE INSIDE OF SAID TUBE, MEANS FOR HOLDING SAID SMALLDIAMETER TUBE WITHIN SAID CONTAINER, WHEREBY THE EXTERIOR SURFACE AND CLOSED END OF SAID TUBE ARE IN CONTACT WITH SAID FLUID FLOWING THROUGH SAID CONTAINER, AND ELECTRODE WITHIN SAID CONTAINER IN CONTACT WITH SOAP FLUID FLOWING THROUGH SAID CONTAINER, A SOURCE OF ELECTRICAL POTENTIAL CONNECTED TO SAID ELECTRODE AND TO SAID TUBE AND SO POLARIZED THAT THE HYDROXYL IONS ARE ATTRACTED TO SAID TUBE, THE OXYGEN MOLECULES SORBED ON THE SURFACE THEREOF, DIFFUSED THERETHROUGH, AND DESORBED ON THE INSIDE THEREOF, AND OXYGEN-PERMEABLE MEMBRANCE CONNECTED TO THE INSIDE OF SAID TUBE SO AS TO RECEIVE THE DESORBED 